Signal transmission system



Dec. 26, 1939. A. WIESSNER 2,184,826

SIGNAL TRANSMISSION SYSTEM Filed Nov. 13, 1931 Patented Dec. 26, 1939 UNITED srArss SIGNAL TRANSMISSION SYSTEM Alfred Wiessner, Berlin, Germany, assigner to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company Application November 13, 1937, Serial No. v174,378

v-A In Germany November 20, 1936 5 Claims.

The present invention relates to high-frequency current systems for intelligence exchange, particularly to systems employing transmission over wires or cables.

The intelligence exchange by means of highfrequency carrier currents over lines or cables is Well known. According to arrangements hitherto known for the abovesaid purposes, generally one side band only has been utilized for transmission, that is to say, behind the modulating equipment there has been provided a filter arrangement, the attenuation of which Was so chosen, that the carrier frequency and one side band were utilized for transmission. It is furthermore known in connection with this type of systems to modulate the carrier frequency by means of push-pull controlled tubes so as to suppress the carrier frequency in the output side. This makes possible either to employ both side bands for transmission,` or to suppress one side band by means of a filter arrangement. Devices of this kind involve certain difficulties with respect to the transmission of the ringing signal, which effectively must differ from the signals used for communication transmission. Such carrier frequency systems transmit the ringing signal as reliably as in a low-frequency intellin gence exchange over lines, for example, by employing impulses of short duration, or a particular tone-frequency. Means must be provided to 'separate the ringing signal from the alternating message currents, and primarily to avoid that the ringing device on'the receiving side be in-Vv fluenced by the message currents. lt is well known to transmit the ringing signal over the communication channel by means of particular tone-frequencies which excite correspondingly tuned relays. However, vthe drawback of this method is that ringing frequencies may be inu cluded in the alternatingmessage currents whereby undesired excitation of the ringing device may occur. To compensate for this drawback, a further known arrangement employs larger amplitudes for the ringing signal than for the message signals, but this measure requires an over-dimensioning of the system, and involves reduced cross-talk attenuation with respect to the other communication channels. Furthermore, this arrangement is inadequate when the line attenuation decreases and the amplitudes of the message signals and the ringing signal assume the same values when the line attenuation increases. Attenuation variations of this magnitude occur in open lines.

According to the invention, it is proposed in connection with systems in which the carrier frequency is partially or entir-ely suppressed, to utin v lize the carrier itself for effecting the ringing signal. This may, for instance, be obtained by interrupting the carrier frequency according to the rhythm of digital impulses. Simultaneously with the carrier frequency, a tone-frequency may also be transmitted so that the ringing will be eifective only when both of said frequencies prevail.

The invention will be more readily understood from the following description in conjunction with the attached drawing, which schematically illustrates the inventive idea of the present application.

in the drawing, a generator l produces a carrier frequency which is modulated in the modulator 2 by alternating message currents, e. g. speech currents, produced by a device 3. The

carrier frequency is' suppressed either in the modulating device, or by a filter Il which is associated with said modulator. One or two side bands which are passed by the filter t are impressed upon the line a., b over an amplifier E, The ringing signals are produced, e. g. by digital impulses from a 'dial switch and are transmitted in such a manner that the carrier frequency' is vderived from the carrier frequency genera-toi` over a special line in which a device is included.

This device is adapted to interrupt the carrier frequency according to the rhythm of the dialling impulses and, for example, to modulatesaid carrier frequency at a tone-frequency lower than 300 cycles per second. This modulated carrier frequency is also supplied to the line a, b.

The lter 4, for instance, may be dimensioned so as to have a passing range for the frequencies between (JOBGQ) and (foi2400) cycles per second. The device 6 alsofincludes a filter which for example has a passing range from the carrier frequency to the carrier plus or minus 300 cycles per second. vFor instance, if the carrier frequency is interrupted in the device 6 by impulses, or if a digit has been selected by a train of impulses, the carrier frequency and the continuous or interrupted tone frequency Will be supplied to the line a, b and impressed upon the amplifier 'l on the receiving side, where said carrier frequency is amplified and applied to the filtering arrangements 8 and 9. The iiltering arrangement 9 is adapted to pass the carri-er frequency foiSOO cycles per second, While the filtering arrangement 8 has a passing range covering the frequency o-I-SOO .to 2400 cycles per second whereby the speed frequency bandis separated from the ringing signals. The alternating message currents from the iiltering arrangement 8 are applied to a demodulator equipment I0 in any known manner, While the ringing signal from the filtering arrangement 9 is impressed upon a device Il Which is adapted to respond e. g. to a frequency lower than 300 cycles per second, or directly to impulses with which the carrier frequency has been modulated,

The arrangement according to the invention as above described requires only a single current source for the ringing signal and communica.- tion transmission, whereby the ringing signal and the message currents may be reliably separated in a simple manner.

What is claimed is:

1. In a high frequency transmission system, a carrier frequency generator, a transmission line, a connection from said generator to one end of said line, a speech frequency modulator and a rst lter in said connection partially at least to suppress the carrier and to lter out all but the side bands above or below the carrier frequency and representing speech frequencies, a.

second connection from said generator to the one end of the line beyond the rst filter, and a second modulator and second filter means in said second connection to modulate the carrier in accordance With a ringing signal to produce side bands of said carrier which side bands are Within the range suppressed by said rst lter.

2. The system according to claim 41 and in which said ringing signal consists of the carrier modulated outside the bands representing speech frequency range.

3. The system according to claim 1 and in which said ringing signal consists of the carrier modulated in accordance with impulses.

4. The system according to claim 1 and in Which said ringing signal consists of the carrier interrupted in accordance with impulses and also modulated with a tone frequency.

5. The system according to claim 1 and in Which said ringing signal consists of the carrier continually transmitted and an interrupted tone signal.

ALFRED WIESSNER. 

